The present invention is directed to enzymes, methods to purify, and obtain such enzymes, amino acid and nucleic acid sequences related thereto, and methods of use for such compositions in genetic engineering applications.
Through the development of plant genetic engineering techniques, it is possible to transform and regenerate a variety of plant species to provide plants which have novel and desirable characteristics. One area of interest for such plant genetic engineering techniques is the production of valuable products in plant tissues. Such applications require the use of various DNA constructs and nucleic acid sequences for use in transformation events to generate plants which produce the desired product. For example, plant functional promoters are required for appropriate expression of gene sequences, such expression being either in the whole plant or in selected plant tissues. In addition, selective marker sequences are often used to identify the transformed plant material. Such plant promoters and selectable markers provide valuable tools which are useful in obtaining the novel plants.
A desirable goal which involves such genetic engineering techniques, is the ability to provide crop plants having a convenient source of wax esters. Wax esters are required in a variety of industrial applications, including pharmaceuticals, cosmetics, detergents, plastics, and lubricants. Such products, especially long chain wax esters have previously been available from the sperm whale, an endangered species, or more recently, from the desert shrub, jojoba. Neither of these sources provides a convenient supply of wax esters. Thus, in order to obtain a reliable source of such compounds, transformation of crop plants, which are easily manipulated in terms of growth, harvest and extraction of products, is desirable.
In order to obtain such transformed plants, however, the genes responsible for the biosynthesis of the desired wax ester products must first be obtained. Wax ester production results from the action of at least two enzymatic activities, fatty acyl reductase and fatty acyl:fatty alcohol acyltransferase, or wax synthase. In addition, a xcex2-ketoacyl-Coenzyme A synthase may also be involved in wax biosynthesis by providing very long chain fatty acyl-CoA substrates for the reductase and wax synthase enzymatic reaction. Preliminary studies with such enzymes and extensive analysis and purification of a fatty acyl reductase, indicate that these proteins are associated with membranes, however the enzyme responsible for the fatty acyl:fatty alcohol ligation reaction in wax biosynthesis has not been well characterized. Thus, further study and ultimately, purification of this enzyme is needed so that the gene sequences which encode the enzymatic activity may be obtained.
It is desirable, therefore, to devise a purification protocol whereby the wax synthase protein may be obtained and the amino acid sequence determined and/or antibodies specific for the wax synthase obtained. In this manner, library screening, polymerase chain reaction (PCR) or immunological techniques may be used to identify clones expressing a wax synthase protein. Clones obtained in this manner can be analyzed so that the nucleic acid sequences corresponding to wax synthase activity are identified. The wax synthase nucleic acid sequences may then be utilized in conjunction with fatty acyl reductase proteins, either native to the transgenic host cells or supplied by recombinant techniques, for production of wax esters in host cells.
Cell-free homogenates from developing jojoba embryos were reported to have acyl-CoA fatty alcohol acyl transferase activity. The activity was associated with a floating wax pad which formed upon differential centrifugation (Pollard et al. (1979) supra; Wu et al. (1981) supra).
Solubilization of a multienzyme complex from Euglena gracilis having fatty acyl-CoA transacylase activity is reported by Wildner and Hallick (Abstract from The Southwest Consortium Fifth Annual Meeting, Apr. 22-24, 1990, Las Cruces, N.Mex.).
Ten-fold purification of jojoba acyl-CoA: alcohol transacylase protein is reported by Pushnik et al. (Abstract from The Southwest Consortium Fourth Annual Meeting, Feb. 7, 1989, Riverside, Calif.).
An assay for jojoba acyl-CoA:alcohol transacylase activity was reported by Garver et al. (Analytical Biochemistry (1992) 207:335-340).
WO 93/10241 is directed to plant fatty acyl-CoA:fatty alcohol O-acyltransferases. A jojoba 57 kD protein is identified as the jojoba fatty acyl-CoA:fatty alcohol O-acyltransferase (wax synthase). The present inventors later reported that the 57 kD protein from jojoba is a xcex2-ketoacyl-CoA synthase involved in the biosynthesis of very long chain fatty acids (Lassner et al. (The Plant Cell (1996) 8:281-292).
Photoaffinity labeling of a 57 kD jojoba seed polypeptide postulated to be an acyl-CoA:fatty alcohol acyltransferase was also reported by Shockey et al. (Plant Phys. (1995) 107:155-160).
U.S. Pat. No. 5,728,412 describes the isolation of genes encoding soluble wax synthase enzymes which are active on short chain alcohols and acetyl-CoA to produce an acetate ester.
By this invention, nucleic acid sequences encoding fatty acyl-CoA: fatty alcohol O-acyltransferase protein (fatty alcohol acyltransferase, E.C.2.3.1.75), are provided, wherein said protein is active in the formation of wax esters from fatty alcohol and fatty acyl substrates. This fatty acyl-CoA: fatty alcohol O-acyltransferase is also referred to herein as xe2x80x9cwax synthasexe2x80x9d. The wax synthase of this invention may be active with a variety of fatty acyl and fatty alcohol substrates, including acyl-CoAs and acyl-ACPs. The carbon chain length of these substrates may vary, although a given wax synthase may show preference for acyl and alcohol substrates having a specific chain length or may be active with acyl and alcohol substrates having a wide range with respect to carbon chain length.
In general, the wax synthase of this invention has activity towards at least those acyl and alcohol substrates having a chain length of from 8 to 26 carbons, although other acyl or alcohol substrates may be tested and further activities discovered. In addition, having obtained the wax synthase protein of this invention, further manipulations are now possible as described in further detail below. These manipulations may lead to production or discovery of other related wax synthases.
In one important aspect of this invention, nucleic acid sequences are provided which encode for wax synthase. Methods are described whereby these sequences may be identified and obtained from the amino acid sequences of the wax synthase proteins of this invention. Uses of the structural gene sequences for isolation of other wax synthase sequences, as well as in recombinant constructs for transcription of wax synthase nucleic acid sequences and/or expression of wax synthase proteins in host cells are described. Uses of other nucleic acid sequences associated with wax synthase protein are also considered, such as the use of 5xe2x80x2 and 3xe2x80x2 noncoding regions.
Thus, this invention encompasses plant wax synthase nucleic acid sequences and the corresponding amino acid sequences, and the use of these nucleic acid sequences in the preparation of oligonucleotides containing wax synthase encoding sequences for analysis and recovery of plant wax synthase gene sequences. The plant wax synthase encoding sequence may encode a complete or partial sequence depending upon the intended use. All or a portion of the genomic sequence, or cDNA sequence, is intended.
Of special interest are recombinant DNA constructs which provide for transcription or transcription and translation (expression) of the plant wax synthase sequences. In particular, constructs which are capable of transcription or transcription and translation in plant host cells are preferred. For some applications a reduction in plant wax synthase may be desired. Thus, recombinant constructs may be designed having the plant wax synthase sequences in a reverse orientation for expression of an anti-sense sequence or use of co-suppression, also known as xe2x80x9ctranswitchxe2x80x9d, constructs may be useful. Such constructs may contain a variety of regulatory regions including transcriptional initiation regions obtained from genes preferentially expressed in plant seed tissue. For some uses, it may be desired to use the transcriptional and translational initiation regions of the wax synthase gene either with the wax synthase encoding sequence or to direct the transcription and translation of a heterologous sequence.
In yet a different aspect, this invention relates to a method for producing a wax synthase in a host cell or progeny thereof via the expression of a construct in the cell. Cells containing a wax synthase as a result of the production of the plant wax synthase encoding sequence are also contemplated herein. Such constructs may employ other nucleic acid sequences which encode for proteins involved in the production of wax esters and/or various fatty,acyl species.
Further, it may be recognized that the wax synthases of this invention may find application in the production of wax esters in such host cells which contain fatty acyl and fatty alcohol substrates of the wax synthase. Such host cells may exist in nature or be obtained by transformation with nucleic acid constructs which encode a fatty acyl reductase. Fatty acyl reductase, or xe2x80x9creductasexe2x80x9d, is active in catalyzing the reduction of a fatty acyl group to the corresponding alcohol. Co-pending U.S. patent application Ser. No. 07/659,975 (filed Feb. 22, 1991), Ser. No. 07/767,251 (filed Sep. 27, 1991) and Ser. No. 07/920,430 (filed Jul. 31, 1992), which are hereby incorporated by reference, are directed to such reductase proteins. This information is also provided in published PCT patent application WO 92/14816. In addition, other sources of wax synthase proteins are described herein which are also desirable sources of reductase proteins.
Especially considered in this aspect of the invention, are plant cells which contain the preferred alcohol substrates of a jojoba wax synthase described herein. A method of providing plant cells with such alcohol substrates is considered wherein said cells are transformed with recombinant nucleic acid constructs which encode a fatty acyl reductase nucleic acid sequence. Thus, plant hosts which do not normally contain significant amounts of the alcohol substrates utilized by wax synthase, may be transformed with a reductase construct such that the alcohols are produced. In this manner, the fatty acyl groups present in the host cell will also provide the source of fatty alcohol substrate utilized by wax synthase in the synthesis of wax esters. Depending on the specificities of the wax synthase and reductase proteins, one recognizes that in this manner, plant cells may be obtained which produce a variety of desirable wax ester products. Such products will have different properties depending on the chain length and degree of saturation of the fatty alcohol and fatty acyl groups. Thus, the wax ester products produced according to the methods herein may be recovered from the host cells and are also considered in this invention.
Also considered in this invention are the modified plants, seeds and wax esters obtained by expression of the plant wax synthase sequences and proteins of this invention.